feat(interruptsource): allow interrupts to use an ssr option

ssr option instructs interrupt sources to ignore targets derived from global context such as window or document so they can be safely used in ssr/universal apps.

If you are using ssr/universal, do not use DEFAULT_INTERRUPTSOURCES. Instead, use createDefaultInterruptSources({ssr: !isPlatformBrowser(platformId) }). See docs or https://stackoverflow.com/a/46893433/64750 for information on how to use isPlatformBrowser.

Fixes #77, #115

Please check if the PR fulfills these requirements

[x] The commit message follows our guidelines: https://github.com/HackedByChinese/ng2-idle/blob/master/CONTRIBUTING.md#pr
[x] Tests for the changes have been added (for bug fixes / features)
[x] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior? (You can also link to an open issue here)

No support for SSR/Universal apps.

What is the new behavior? Adds an opt-in option when creating interrupt sources that will allow compatibility with SSR/universal.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[x] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

moribvndvs / ng2-idle

feat(interruptsource): allow interrupts to use an ssr option #130